<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<style>
    .box{
        width: 5rem;
        height: 100px;
        background: red;
    }
</style>
</head>
<body>
    <div class="box"></div>
</body>
</html>